CHANGES IN CHLOROPHYLL-A CONCENTRATION AS AN INDICATOR OF PRIMARY PRODUCTIVITY IN WATERS BEFORE AND AFTER SEA FENCING ON THE COAST OF TANGERANG, INDONESIA

Najwa ELZAHRA , Luthfi ANZANI , Yulius YULIUS , Muhammad RAMDHAN , Dini PURBANI , Aprizon PUTRA , Taslim ARIFIN , Hadiwijaya L. SALIM , Anang D. PURWANTO , Joko PRIHANTONO , Rinny RAHMANIA , Sri Endah PURNAMANINGTYAS , Herlina Ika RATNAWATI

DOI: 10.21163/GT_2026.211.01

ABSTRACT: Coastal eutrophication is an escalating concern in Indonesian estuaries, driven by anthropogenic pressures and physical interventions such as sea fencing. This study analyses the spatial and temporal changes in Chlorophyll-a (Chl-a) concentrations and Net Primary Productivity (NPP) in the coastal waters of Kronjo, Tangerang Regency, before (2020) and after (2024) the installation of illegal sea fences. High-resolution (3 m) PlanetScope satellite imagery was processed using the Normalised Difference Chlorophyll Index (NDCI) and subsequently modelled into NPP using the Vertically Generalised Productivity Model (VGPM), incorporating supporting data such as Photosynthetically Active Radiation (PAR), Sea Surface Temperature (SST), and Euphotic Zone Depth (Zeu). Despite an increase in localised maximum values, the results revealed a slight decrease in mean Chl-a concentrations from 6.12 to 5.89 mg/m³. The spatial distribution of NPP became more homogenised, with high-value areas becoming more spatially constrained. A robust Pearson correlation (r = 0.99; p < 0.001) between Chl-a and NPP confirms the reliability of NDCI for capturing primary productivity dynamics. This study demonstrates the efficacy of high-resolution remote sensing in evaluating the ecological impacts of coastal physical structures and informing spatially explicit management strategies. This is the first high-resolution remote sensing study assessing Southeast Asia’s pre- and post-se fencing impacts, highlighting the critical need for integrated spatial monitoring in tropical estuarine ecosystems.

Keywords: Chlorophyll-a; Estuarine monitoring; PlanetScope; Primary productivity; Sea fence.

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